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General Comments

Zinc alloy diecastings can be joined to other components by most available techniques. However fusion welding is best avoided as being impractical as a manufacturing technique and soldering is only applicable to pre-plated castings.

The good ductility of zinc diecastings allows them to be post formed to provide permanent fixing to mating components, for example by incorporating cast in rivet features or a lip or lug which can be spun or bent over. This capability is widely utilised proving its practicality and with reasonable care in design of casting and the forming tools such fixing methods will work first time.

When designing features that are to be post formed and choosing the forming method there are a number of factors that should be born in mind.

Wherever possible form the material in compression rather than tension, this will generally produce a more consistent result, as it is less demanding of the physical quality of the casting. If some tensile extension is unavoidable keep the strain below about 5%, eg do not bend a wall section around too narrow a radius.

Do not perform forming operations on very cold castings ie below normal factory ambient temperatures.

Expect the formability of the casting to change in the first few weeks after casting. It will be most formable within about 24 hours after casting but ageing affects reduce this capability rapidly, followed within a few weeks by an increase in formability but not back to the excellence shown immediately after casting. The normal pace of manufacturing means that production castings frequently have to be formed when they are in their least amenable condition. Nevertheless well-designed features are still reliably formed by properly thought out processes. However this factor should be considered when prototype and pre-production diecastings are undergoing forming trials as they may be at a more favourable age than will be the case for production. In other words successful forming of a very new or fairly old casting will not guarantee that the forming process is suitable for castings of an intermediate age.

Forming processes which locally induce some heat in the casting eg spin or wobble riveting and spinning over of lips, allow significantly higher deformations to be reliably achieved.

As with most castings much use is made of threaded fasteners to attach zinc diecastings to each other or to other materials. Zinc diecastings offer an advantage in that it is not usually necessary to drill the casting to provide either through holes for bolts, or holes to be tapped, or for self-tapping screws. Likewise zinc diecastings can usually be cast sufficiently precisely to allow interference fitting with other parts without any prior machining.

Adhesive bonding is perfectly practicable with zinc alloys but it is only rarely used, probably because in most circumstances it would be beaten on cost and speed by a simple forming process.

Another point which is not covered in detail in this section but that should not be forgotten is the ability to incorporate inserts in the casting or to overmould the casting with plastic. To date not much use has been made of the latter technique but it must have a lot to offer in appropriate applications.

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